This preview shows page 1. Sign up to view the full content.
Unformatted text preview: tion of
entropy
generation Q
Tsurr (b) The wall is considered Q
Tsys Q Q
Tsurr (c) The wall as well as
(c) the variations of temperature
(c) in the system and the
(c) surroundings are considered FIGURE 7–70
Graphical representation of entropy generation during a heat transfer process through a finite temperature difference. cen54261_ch07.qxd 11/18/03 9:57 AM Page 332 332
FUNDAMENTALS OF THERMALFLUID SCIENCES SUMMARY
The second law of thermodynamics leads to the definition of a
new property called entropy, which is a quantitative measure of
microscopic disorder for a system. The definition of entropy is
based on the Clausius inequality, given by
Q
T 0 1. Pure substances:
s
s2 Any process:
Isentropic process: s1 s2
s1 (kJ/kg · K) (kJ/K)
2. Incompressible substances: where the equality holds for internally or totally reversible
processes and the inequality for irreversible processes. Any
quantity whose cyclic integral is zero is a property, and entropy
is defined as
dQ
T dS s1
T2 Isentropic process: Cav ln T2
T1 T1 (kJ/kg · K) (kJ/K)
int rev For the special case of an internally reversible, isothermal process, it gives
S s2 Any process: Q
T0 3. Ideal gases:
a. Constant specific heats (approximate treatment):
Any process:
s2 s1 Cυ, av ln T2
T1 R ln υ2
υ1 (kJ/kg · K) s2 s1 Cp, av ln T2
T1 R ln...
View
Full
Document
This document was uploaded on 11/28/2012.
 Spring '09

Click to edit the document details